This invention relates to correction circuits for correcting the output signals produced by fluid flowmeters of the type which can be arranged to produce an electrical pulse output signal whose pulse repetition rate is representative of the volumetric flow rate of the fluid whose flow rate is being measured by the flowmeter, the correction being effected in dependence upon at least one other parameter of the fluid, for example its temperature and/or pressure. Flowmeters of this type will hereinafter be referred to as flowmeters of the type defined, and a typical example is a turbine flowmeter. The invention is more particularly, but not exclusively, concerned with such correction circuits for correcting the output signals produced by gas flowmeters of the type defined, in dependence upon the temperature of the gas.
When measuring the total volume of gas flowing through a pipe by means of a gas flowmeter of the type defined, it is often necessary to correct the volume measurement in dependence upon the temperature and pressure of the gas, although under certain circumstances a temperature correction alone is sufficient. For this temperature correction, the volume measurement is corrected so as to determine the volume the gas would have occupied had it been constantly at a reference temperature, which is typically 60.degree. F (15.5.degree. C) for the United Kingdom.
In turbine or like flowmeters which are arranged to drive a mechanical total volume counter via a gear train, it is known to effect the temperature correction by including in the gear train an infinitely variable transmission whose transmission ratio varies in dependence upon the temperature of the gas. However, such a mechanical arrangement is relatively complex and consequently tends to be unreliable. Additionally, it is both difficult and expensive to retro-fit an existing flowmeter, not having a temperature correction facility, with a temperature-responsive variable ratio transmission. It is therefore an object of the present invention in one of its aspects to provide an electrical correction circuit for correcting the output signal of a flowmeter of the type defined in dependence upon a parameter, for example the temperature, of the fluid passing through the flowmeter.
When a gas flowmeter of the type defined is used to measure the total volume of gas flowing through a pipe, as outlined above, it is frequently located in a place at which a mains electricity supply is not readily available. It is therefore an object the invention in another of its aspects to provide such a correction circuit having a relatively low power consumption, thus rendering it suitable for operation for long periods with its power supply provided by primary cells.